1. Field of the Invention
The present invention relates to a thin film transistor structure and the method for making the same and, more particularly, to a thin film transistor structure for a field emission display and method for making the same.
2. Description of Related Art
Display panels have become more and more important in our daily lives. People transmit information by means of the display panels when using computers and the Internet, as well as TV sets, cell phones, personal digital assistants (PDAs), automobile information systems, etc. Considering weight, volume, of display panels, and users' health, more and more people choose to use flat panel displays instead of cathode-ray-tubes. Among the burgeoning types of display panels, the field emission display has the advantage of high image quality found with the conventional cathode ray tube display. Also, the field emission display has advantages of high yield, fast reacting time, good performance in displaying coordination, having high brightness over 100 fL, light and thin structure, wide range of color temperature, high mobile efficiency, excellent distinguishability of tilted direction, etc. in comparison with the conventional liquid crystal display that has the disadvantages of blurred view angle, limited range of usable temperature, and slow reacting time. Moreover, the field emission display emits light spontaneously. Through the construction of a high efficiency fluorescent film, the field emission display provides outstanding brightness performance even outdoors so it is thought as a quite competitive display panel and is even likely to replace the liquid crystal display.
The principle of the field emission display is similar to that of the traditional cathode-ray-tube display. They both emit electrons to hit the fluorescent medium on a substrate in vacuum. As for the structure, the cathode-ray-tube display emits electron beams by a single electron gun and controls the direction of the electron beams by using a polarization plate. However, the field emission display is composed of hundreds of thousands of active cold emitters, each of which corresponds to a pixel independently, so no polarization plate is needed. As for the working voltage, the cathode-ray-tube display needs a voltage around 15 to 30 kV. On the other hand, the cathode voltage of a field emission display is only less than 1 kV.
U.S. Pat. No. 6,525,453 disclosed a field emission display composed of a plurality of thin film transistors 22, a plurality of carbon nanotubes 24, and a transparent electrode 38 having a fluorescent layer 39, as shown in FIG. 1 of this application. The carbon nanotubes 24 connect the drain electrode 32 of the thin film transistor 22 through the channel 42. However, there is only a thin film transistor 22 for controlling the current of the field emission display in a pixel. When the anode bias is increased and the current through the field emission display is cut off, an extremely large voltage will punch off the device or a gate dielectrics breakdown will occur. As a result, the transistor loses efficacy and the pixel of the field emission display is unable to operate normally.
Therefore, it is desirable to provide a thin film transistor structure for a field emission display to mitigate and/or obviate the aforementioned problems.